1. Field of the Invention
The present invention relates to self-inerting fuel processing systems, methods of shutting down such fuel processing systems, and fuel cell electric power generation systems incorporating them.
2. Description of the Related Art
Fuel cell electric power generation systems comprising a fuel cell stack and a fuel processing system for converting a fuel into a hydrogen-rich reformate stream and supplying it to the fuel cell stack can be operated to provide electric power.
On shutdown of such fuel cell electric power generation systems, the fuel processing system and (optionally) the fuel cell stack are typically purged of reactant gases, including residual fuel, reformate and other reaction products. Purging is typically performed using an inert gas stream, such as nitrogen.
Purging the anode passages of the fuel cell stack assists in preventing electrochemical reactions from proceeding within the fuel cells on shutdown, such as the generation of water at the cathodes. It also reduces the electric potential of the stack, which may be desirable in some applications.
Typical fuel processing components in such systems include reformers, such as steam reformers, for example, and may also include shift reactors and/or selective oxidizers. These components are purged to reduce deterioration of the components that can occur when reactant gases are present in them at temperatures below their normal operating temperatures. The presence of reactants at lower temperatures can result in carbon deposition and/or water condensation on the catalyst bed(s) of the component(s) and carbonyl formation, for example.
Conventional fuel cell electric power generation systems typically employ pressurized nitrogen supplied from a nitrogen gas cylinder for purging. This approach undesirably increases the size and weight of the overall electric power generation system and requires maintenance to exchange an empty gas cylinder with a new one. Further, the operating cost of the electric power generation system is increased due to the expense of the inert gas supply.
A self-inerting fuel processing system is provided. In one embodiment, the present fuel processing system comprises:
(a) a fuel processor comprising a reformer for reforming a fuel to a reformate stream comprising hydrogen;
(b) at least one self-reducing catalyst bed;
(c) a recycle loop for circulating a gas stream through the fuel processor and the self-reducing catalyst bed(s) during shutdown of the fuel processing system; and
(d) an oxidant supply for introducing oxidant into the recycle loop during shutdown of the fuel processing system.
A method of shutting down the present fuel processing system is also provided. In one embodiment, the present method comprises:
(a) interrupting supply of fuel to the fuel processor;
(b) introducing an oxidant into the recycle loop;
(c) removing at least a portion of the oxygen in the introduced oxidant by oxidizing the self-reducing catalyst bed(s) to produce a substantially inert gas stream;
(d) purging reaction gas from the fuel processor, wherein the reaction gas comprises fuel, reformate, or both; and
(e) circulating the substantially inert gas stream in the recycle loop.
A self-inerting fuel cell electric power generation system is also provided. In one embodiment, the present electric power generation system comprises:
(a) a fuel processor comprising a reformer for reforming a fuel to a reformats stream comprising hydrogen;
(b) at least one self-reducing catalyst bed;
(c) a fuel cell stack fluidly connected to the fuel processor for receiving the reformate stream;
(d) a recycle loop for circulating a gas stream through the fuel processor and the self-reducing catalyst bed(s) during shutdown of the fuel processing system; and
(e) an oxidant supply for introducing an oxidant into the recycle loop during shutdown of the fuel processing system.